1. Technical Field
The technical field of the present disclosure relates to a wireless transmission system for transmitting data of pictures, sounds, images, and the like by wireless communication.
2. Description of Related Art
Television sets having light weight such as an LCD (Liquid Crystal Display) TV set or a PDP (Plasma Display Panel) TV set have become commonplace in many homes. Such lightweight TV sets can be moved in a house more easily than before. In order to watch pictures on a TV set, it is necessary to use a device that can provide picture contents (a picture contents providing device) such as a DVD player, a digital cassette recorder or a tuner, so that picture contents are sent to the TV set.
Usually, picture contents travel in a cable from the picture contents providing device to the TV set. Recently, a wireless LAN (wireless Local Area Network) can be used instead of the cable for transmitting picture contents from the picture contents providing device to the TV set.
Conventionally, a cable that transmits picture contents is necessary so that pictures can be displayed on the TV set. Therefore, it is necessary to lay an antenna cable in a room where the TV set is installed for watching television. However, if picture contents can be transmitted via the wireless LAN, such a cable becomes needless so that the TV set can be moved in a house freely without limiting the installation place. This advantage has received attention recently, and the wireless transmission of pictures utilizing the wireless LAN has been becoming widely available gradually. As a standard of the wireless LAN, there is IEEE (Institute of Electrical and Electronic Engineers) 802.11, for example. As a standard of the transmission of pictures and sounds on the IP (Internet Protocol), there is RTP (Real-time Transport Protocol), for example.
In addition, JP-A-2003-163846 (hereinafter referred to as a patent document 1) discloses a technique for adjusting approximately a directivity of a picture signal transmission channel by utilizing a test picture displayed on a display of a receiver.
In addition, JP-A-2005-26733 (hereinafter referred to as a patent document 2) discloses a wireless communication device equipped with a first communication means for transmitting and receiving a non-directional communication wave, a second communication means for transmitting and receiving a directional communication wave and a transmission and reception data control means for performing a control such that a low rate data is transmitted and received by the first communication means while a high rate data is transmitted and received by the second communication means.
In order to perform a transmission of pictures via a wireless LAN utilizing a radio wave, it is necessary to provide a picture receiver of a TV set or the like and a picture transmitter of a DVD player or the like with a device for wireless LAN. The device for wireless LAN may be embedded as a wireless LAN module in the picture receiver and the picture transmitter, or it is prepared as an external option to be connected to the picture receiver and the picture transmitter. In either case, power consumption is more than a conventional device since the device for wireless LAN is added. It is important to reduce power consumption as much as possible to make an environment friendly product.
A plurality of wireless LANs using the same radio wave channel may cause interference between them. Therefore, if the wireless LANs using the same radio wave channel are arranged closely to each other, throughputs of the wireless LANs may be restricted. When using a non-directional antenna that has a wide reaching area of the radio wave for obtaining an appropriate throughput with a radio wave of the same channel, it is necessary to cover a corresponding distance (approximately 50 meters for example). In other words, it is difficult to obtain throughputs that are inherent to the wireless LANs using a non-directional antenna in a house if they utilize the same radio wave channel.
Note that the example of conventional structure disclosed in the above patent document 1 or 2 cannot solve the above-mentioned problem (or is insufficient as a solution of the problem).